1. Field of the Invention
The present invention is directed generally to the printing arts. More particularly, this invention pertains to improved apparatus for effecting the transfer of printed material from an impression cylinder to a chain delivery mechanism of the type employed in a conventional offset printing system.
2. Description of the Prior Art
In the offset printing art, conventional arrangements feature the use of rotatable, contacting blanket and impression cylinders to effect the transfer of a desired image onto sheets of paper guided therebetween. After travelling through the point of contact between the surfaces of these cylinders, the imprinted material is then grasped at an edge by means of "grippers", well-known in the offset printing art, and advanced by means of a chain delivery mechanism, also well-known in the art, to thereby pull and, when appropriate, release the printed material. The chain delivery includes a pair of opposed continuous chains that circulate between pairs of sprockets, one of such pairs of sprockets being engaged to and driven by a motor. The various elements of the system are appropriately synchronized so that the printed matter is grabbed by the gripper, removed at an appropriate rate and thereafter released. At the same time, a new sheet is received by the blanket and impression cylinders without undue delay. The gripper continually repeats a cycle of grabbing and releasing sheets to cause the printed material to be accumulated in a pile.
A recognized problem with systems such as the star wheel system is that while wrinkling is minimized smudging or marking occurs as the printed material is transferred from the rotating cylinders to the grippers. Various attempts have been made to prevent such smudging of the freshly-printed material. Representative attempts include the air cushion drum. The air cushion drum, while eliminating the smudging problem of the star wheel, requires large amounts of energy with attendant high operating costs; is difficult to maintain as the mesh-like surface of the drum is frequently clogged by debris; and is cost prohibitive to retrofit existing printing equipment.
Various attempts to overcome the disadvantages of the star wheel have included the provision of bars having paper contacting means mounted thereon and arranged transverse to the circulating chains of the chain delivery U.S. Pat. No. 2,025,481 of Stussi entitled "Sheet Delivery Device For Cylinder Printing Presses" represents such a system. The shortcomings of the system disclosed in this patent are discussed extensively in the above-referenced parent to this continuation-in-part application. That apparatus overcomes significant disadvantages of the prior art as typified by the Stussi patent by providing a paper guiding mechanism for attachment to a chain delivery which employs a pair of opposed clips, each of which is detachably mounted to preselected links of the circulating chains of the chain delivery (avoiding any need for the addition of a protrusion on the link or to the pintle as taught by Stussi). The clips support the bar which is thereby arranged transverse to the continuous chains of the chain delivery. At least one paper contacting member is provided having an eccentric shape and including a single bearing surface at a defined apex. The paper contacting member cooperates generally with the bar, allowing it to be held at a predetermined, adjustable position. By adjusting the orientation of the apex, the point of contact of the printed matter emergent from the impression and blanket cylinders can be preferentially varied.
While the invention described and claimed in the parent application overcomes significant problems, the applicant has found that, in operation, the clip disclosed therein, including an upper flange 30, integrally formed with the top portion 28 of the clip in combination with a lower flange 38, impose significant compressive forces transverse to the vertical (inner) side members of the links of the chains to which are attached. Such compressive forces may restrict the mobility of the chains, resulting in the retention of crimps which result from the passage of the chain over the sprockets of the chain delivery mechanism. Such undesired distortion of the shape of the chain may, in fact, cause it to go off track. Additionally, while the particular eccentric shape of the paper contacting elements of the invention disclosed in the parent application has proven advantageous, the Applicant has found that the existence of a large variety of printing mechanisms results in a need for greater adjustability of the point of contact with the printed material.